1. Field of the Invention
The present invention relates to a wireless communications system provided with a hand-over (automatic change-over of an access point with respect to a terminal) for engaging in wireless communications with an access point. Then, the present invention relates to a technology for guaranteeing QoS (quality of service) in this kind of wireless communications system.
2. Description of the Related Art
This kind of wireless communications system allows a terminal to move between service areas of an access point.
Then, when the terminal moves from a service area of the access point to a service area of the next access point, the connection of the terminal is automatically changed over (handed over) to the next access point.
That is, in this kind of wireless communications system, the terminal has a hand-over function.
Furthermore, as seen from the next access point, this terminal which has moved to its own service area is a new terminal. Here, when no existing terminal which is already connected to this access point is present, no malfunction is caused even when the new terminal is connected to this access point.
However, when there is an existing terminal which is already connected to the next access point, some malfunctions may be caused in the wireless communications in a competition between the existing terminal and new terminal.
Hereinafter, this point will be explained by citing an example. FIG. 8 is a schematic view of a conventional wireless communications system.
In the wireless communications system shown in FIG. 8, there are two terminals; a terminal 1 and a terminal 2.
At present, terminal 1 exists in the service area of access point 3 to be connected therewith. Furthermore, terminal 2 exists in the service area of access point 4 to be connected therewith.
An access point 3 and terminal 1, and access point 4 and terminal 2 are connected by a link having a transmission bandwidth of 10 Mbps. To terminal 1 and terminal 2, packets 6 and 7 of the image data (MPEG 2: 6 Mbps) with the same priority (here, the priority is “medium”) are transmitted.
Furthermore, packet transmission device 5 has an access point 3 and an access point 4 under the control of the device. Packet transmission device 5 and access point 3, and packet transmission device 5 and access point 4 are connected by a communications line of 100 Mbps. Furthermore, for guaranteeing QoS, either or all of packet transmission device 5, access point 3, and access point 4 are provided with QoS guarantee means which is configured of a scheduler, a shaper, and a queue. With the QoS guarantee means, the priority of the packet which flows through the wireless communications system shown in FIG. 8 is controlled.
Furthermore, the “packet transmission device 5” described here has various forms such as a gateway (including a home gateway), a router, a switch or a board which serves as a major function. However, any form will do.
Then, in the condition shown in FIG. 8, only communications less than the transmission bandwidth is provided with respect to any of the terminals. Consequently, both terminal 1 and terminal 2 can receive communications without any malfunction at all.